Study of Influence of Electrode Geometry on Impedance Spectroscopy

Electrochemical Impedance Spectroscopy (EIS) is a powerful and proven tool for analyzing AC impedance response. A conventional three electrode EIS method was used to perform the investigation in the present study. Saturated potassium chloride solution was used as the electrolyte and three different material rods were used as working electrodes. Different configurations of electrode area were exposed to the electrolyte as an active area to investigate electrode geometry effects. Counter to working electrode distance was also altered while keeping the working electrode effective area constant to explore the AC response dependence on the variation of ion travel distance. Some controlled experiments were done to validate the experimental setup and to provide a control condition for comparison with experimental results. A frequency range of 100 mHz to 1 MHz was used for all experiments. In our analysis, we have found a noteworthy influence of electrode geometry on AC impedance response. For all electrodes, impedance decreases with the increase of effective area of the electrolyte. High frequency impedance is not as dependent on geometry as low frequency response. The observed phase shift angle drops in the high frequency region with increased working electrode area, whereas at low frequency the reverse is true. Resistance and capacitive reactance both decrease with an increase of area, but resistance response is more pronounce than reactance. For lower frequencies, small changes in working area produce very distinctive EIS variations. Electrode material as well as geometry was systematically varied in the present study. From these and other studies, we hope to develop a fundamental foundation for understanding specific changes in local geometry in fuel cell (and other) electrodes as a method of designing local morphology for specific performance.

Preparation and Characterization of Nanocomposite Calcium Doped Ceria Electrolyte With Alkali Carbonates (NK-CDC) for SOFC

The entire world’s challenge is to find out the renewable energy sources due to rapid depletion of fossil fuels because of their high consumption. Solid Oxide Fuel Cells (SOFCs) are believed to be the best alternative source which converts chemical energy into electricity without combustion. Nanostructured study is required to develop highly ionic conductive electrolyte for SOFCs. In this work, the calcium doped ceria (Ce0.8Ca0.2O1.9) coated with 20% molar ratio of two alkali carbonates (CDC-M: MCO3, where M = Na and K) electrolyte was prepared by co-precipitation method in this study. Ni based electrode was used to fabricate the cell by dry pressing technique. The crystal structure and surface morphology was characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). The particle size was calculated in the range of 10–20nm by Scherrer’s formula and compared with SEM and TEM results. The ionic conductivity was measured by using AC Electrochemical Impedance Spectroscopy (EIS) method. The activation energy was also evaluated. The performance of the cell was measured 0.567W/cm2 at temperature 550°C with hydrogen as a fuel.

Nafion/PBI Nanofiber Composite Membranes for Fuel Cells Applications

The PBI (poly(benzimidazole)) nano-fiber thin film with thickness of 18–30 μm is prepared by electro-spinning from a 20 wt% PBI/DMAc (N, N′-dimethyl acetamide) solution. The PBI nano-fiber thin film is then treated with a glutaraldehyde liquid for 24h at room temperature to proceed chemical crosslink reaction. The crosslink PBI nano-fiber thin film is then immersed in Nafion solutions to prepare Nafion/PBI nano-fiber composite membranes (thickness 22–34 μm). The morphology of the composite membranes is observed using a scanning electron microscope (SEM). The mechanical properties, conductivity, and unit fuel cell performance of membrane electrode assembly (MEA) of the composite membrane are investigated and compared with those of Nafion-212 membrane (thickness ∼50 μm) and Nafion/porous PTFE (poly(tetrafluoro ethylene)) composite membrane (thickness ∼22 μm). We show the present composite membrane has a similar fuel cell performance to Nafion/PTFE and a better fuel cell performance than Du Pont Nafion-212.

Electrochemical Performance of Ni-YSZ, Ni/Ru-GDC, LSM-YSZ, LSCF and LSF Electrodes for Solid Oxide Electrolysis Cells

The electrochemical performance of solid oxide electrolysis cells (SOECs) having nickel – yttria stabilized zirconia (Ni-YSZ) hydrogen electrode and a composite lanthanum strontium manganite – YSZ (La0.8Sr0.2MnO3−δ – YSZ) oxygen electrodes has been studied over a range of operating conditions temperature (700 to 900°C). Increasing temperature significantly increased electrochemical performance and hydrogen generation efficiency. Durability studies of the cell in electrolysis mode were made over 200 h periods (0.1 A/cm2, 800°C, and H2O/H2 = 70/30). The cell significantly degraded over the time (2.5 mV/h). Overpotentials of various SOEC electrodes were evaluated. Ni-YSZ as a hydrogen electrode exhibited higher activity in SOFC mode than SOEC mode while Ni/Ru-GDC presented symmetrical behavior between fuel cell and electrolysis mode and gave lower losses when compared to the Ni-YSZ electrode. All the oxygen electrodes gave higher activity for the cathodic reaction than the anodic reaction. Among the oxygen electrodes in this study, LSM-YSZ exhibited nearest to symmetrical behavior between cathodic and anodic reaction. Durability studies of the electrodes in electrolysis mode were made over 20–70 h periods. Performance degradations of the oxygen electrodes were observed (3.4, 12.6 and 17.6 mV/h for LSM-YSZ, LSCF and LSF, respectively). The Ni-YSZ hydrogen electrode exhibited rather stable performance while the performance of Ni/Ru-GDC decreased (3.4 mV/h) over the time. This was likely a result of the reduction of ceria component at high operating voltage.

Dynamic Analysis of a Planar SOFC Stack Fuelled by Biogas

This paper analyzes the dynamic behaviour of a 50 kW stack using planar co-flow solid oxide fuel cells with direct internal reforming fuelled by a biologically derived gaseous mixture of methane and carbon dioxide. The system modelled is composed by the SOFC stack, a catalytic burner, the heat recovery system and the control device aimed to keep the air temperature at the stack exit and the fuel utilization near to the set values. The model has been implemented using standard and user-defined components of an a-causal software based on the open-source Modelica modelling language. After a brief introduction to the production of the gaseous fuel derived from the anaerobic digestion of pig manure, data obtained from a case study on a pig farm situated in Lombardia (Italy) are presented, focusing on the yield of methane which can be exploited. The steady-state performance of the SOFC system fuelled by pure methane are compared with those obtained for the biogas working conditions, showing that the stack voltage is affected by greater concentration losses. Then, starting from a steady-state delivered current of 750 mA cm−2, the dynamic behaviour of the system when a load change of −150 mA cm−2 occurs is investigated for both pure methane and biogas fuelling hypothesis. The results of the simulations show that the transient phase is only marginally affected by the composition of the fuel, which causes a delay of about 50 s in the voltage transient. Finally, the effect obtained by imposing a linear variation in the fuel composition, which can be representative of a modification in the biological degradation of the organic substrate within the anaerobic digester, is discussed. After an initial transient, which is comparable with that obtained for a variation in the load current, the SOFC system is capable to restore the initial delivered power, provided that the required amount of fuel can be supplied to the anode.

Effect of Flow Channel Design on Planar SOFC Performance

For a planar SOFC interconnect, channel design parameters such as channel width, depth, numbers, wall conditions, etc. are strongly related to the overall cell performance in the way of fuel utilization. Heat and mass transfer rate can be improved by flow mixing enhancement in the properly designed flow channel. In this paper, the influence of flow channel parameters on cell performance in SOFC is discussed. The flow aerodynamic characteristics and friction loss from the bottom surface geometry considered using a three-dimensional computational modeling method. Specially the effect of channel depth and channel mixing on performance and fuel utilization is investigated with an in-depth analysis. As well as a simplified single channel to see the detailed phenomena, an interconnect including whole channels and manifold hole are simulated. The results including a comparison between experimental data and simulation show that to reduce side loss enhanced cell performance with flow and temperature distribution. Based on the result of channel modeling, single cell test with modified design is conducted to achieve performance improvement. This work can be helpful in understanding the channel flow and provide a valuable guideline to channel design for a planar SOFC.

Fuel Cells and Hydrogen Education at Michigan Technological University

There is a strong need for a transformative curriculum to train the next generation of engineers who will help design, construct, and operate fuel cell vehicles and the associated hydrogen fueling infrastructure. In this poster we discuss how we integrate fuel cell and hydrogen technology into the project-based, hands-on learning experiences in engineering education at Michigan Technological University. Our approach is to involve students in the learning process via team-based interactive projects with a real-world flavor. This project has resulted in the formation of an “Interdisciplinary Minor in Hydrogen Technology” at Michigan Technological University. To receive the 16 credit minor, students are required to satisfy requirements in four areas, which are: • Participation in multiple semesters of the Alternative Fuels Group Enterprise, where students work on hands-on integration, design, and/or research projects in hydrogen and fuel cells. • Enrolling in a fuel cell course. • Enrolling in a lecture or laboratory course on hydrogen energy. • Enrolling in discipline-specific elective courses.

Partial Impedance Spectroscopy Tests of a 6 kW Proton Exchange Membrane Water Electrolyzer Stack

Impedance characteristics of a 6 kW proton exchange membrane (PEM) electrolyzer stack are presented under various operating conditions. An electrolyzer stack was operated under room temperature and partial current range (0 to 80 A). The whole stack impedance spectrums were measured by three different power supply configurations. The total sweeping frequency range (0.5 Hz to 20 kHz) is divided into low frequency (0.5 to 20 Hz), middle frequency (20 Hz to 1 kHz), and high frequency (1 to 20 kHz). Each frequency range required a different measurement setup to measure the whole stack impedance data. In this study, the partial impedance spectrums at low and high frequency ranges are successfully measured and analyzed. The measured data is verified with Kramers-Kronig relations. Measurement issues at the middle frequency region are discussed.

Catalytic Material Development for a SOFC Reforming System: Application of an Oxidative Steam Reforming Catalyst to a Monolithic Reactor

The main objective of this work was to develop fuel reforming technologies to produce a H2-rich synthesis gas to power a solid oxide fuel cell being developed by US DOE for applications like diesel auxiliary power units. In order to accomplish this objective the following efforts were required: 1) examination of the effect of oxygen-conducting supports on reforming catalyst performance, 2) demonstration of the long-term stability under reforming conditions of an oxide powder catalyst deposited onto an oxygen-conducting support, 3) fabrication of a catalyst system by depositing the active catalyst and oxygen-conducting material onto a monolithic support structure for scaled-up reforming tests, 4) demonstration of the scaled-up reforming tests using the monolithic reactor. A successful 1,000-hr diesel reforming test was completed on a powder pyrochlore catalyst developed by NETL deposited onto an oxygen-conducting support. This test demonstrated that the catalyst and support compositions developed have significant potential in a commercial reforming application for the production of synthesis gas. Transforming this powder catalyst into a commercially viable form was the next major step to the development of a usable product. An alumina monolith structure coated with both the oxygen-conducting support and the active pyrochlore phase was fabricated and its performance was validated by short term partial oxidation (POX) tests on pump diesel, and in an integrated reformer-fuel cell test for 100 hrs on a biodiesel fuel under oxidative steam reforming (OSR) conditions.